A. Field of the Invention
The present invention relates to a method of forming a protective film of a slide-resistant member or a wear-resistant member, and to a slide-resistant member having a protective film formed by the method. In particular, the present invention relates to a method of forming a protective film of a magnetic recording medium, and to a magnetic recording medium having a protective film formed by the method.
B. Description of the Related Art
A protective film of mainly carbon is used as a hard coating film that constitutes a surface portion of a slide-resistant member or a wear-resistant member. In the field of magnetic recording, for example, slide-resistance or wear-resistance is necessary because of contact between a magnetic recording medium and a magnetic head. For a protective film of a magnetic recording medium or a magnetic head, a film mainly composed of carbon (hereinafter referred to as “a carbon film”) is used.
A carbon protective film is composed of diamond-like carbon (DLC), tetrahedral amorphous carbon (ta-C), amorphous carbon (a-C) or the like. Among them, a DLC film is suited for a surface coating film owing to smoothness and high hardness of its surface. Known methods of forming a carbon film include sputtering, plasma CVD, and so on.
A carbon film formed by a plasma CVD method (hereinafter referred to as “p-CVD carbon film”) is denser and harder as compared with a carbon film formed by a sputtering method, and so, superior in durability and corrosion resistance. The p-CVD carbon film, being formed from hydrocarbon radicals, tends to have a rigid three-dimensional tetrahedral structure through the hydrogen, which brings about the superiority. For this reason, a protective film in a magnetic recording medium today is composed of a p-CVD carbon film, in particular, a DLC film. Although a p-CVD carbon film is beneficial in durability and corrosion resistance, the p-CVD carbon film is unfavorable for restraining gas adsorption on the surface of the protective film, because hydrogen existing on the surface of the p-CVD carbon film can be an adsorption site for gas such as SO2. To restrain gas adsorption on a surface of protective film, studies have been done including a method disclosed in Japanese Patent Unexamined Publication No. Hei9-128732, in which a carbon film deposited by sputtering is laminated on a p-CVD carbon film, and a method disclosed in Japanese Patent Unexamined Publication No. 2004-288327, in which the surface of a p-CVD carbon film is subjected to plasma treatment under an atmosphere of mixed gas of rare gas and oxygen.
However, the method in which a carbon film deposited by sputtering is laminated on a p-CVD carbon film involves a problem of increased thickness of the protective film. This is undesirable because, in a magnetic recording medium, for example, the thick protective film increases a magnetic spacing that is the spacing between a magnetic recording layer of the magnetic recording medium and a read/write element of a magnetic head, and this degrades read/write performance. It is another problem to require an additional manufacturing step of the plasma treatment after deposition of a p-CVD carbon film.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.